The Source and Nature of Transient Surges

Sources of transient voltages or surges due to various phenomena normal to the power station environment are described along with typical waveforms and other parameters of the surges coupled into control circuits. The mechanism by which surges are generated by switching of inductive devices in low voltage control circuits is described in detail. The importance of the contact restrike action in creating and coupling very short duration transients onto the control bus is evident. Oscillograms of such a transient generated by operation of a typical auxilary relay circuit are included.     

Interaction of drive modulation and cable parameters on AC motortransients

This paper investigates overvoltage transients on AC induction motors when connected through a cable of arbitrary length to a variable frequency drive (VFD) consisting of a pulsewidth modulation (PWM) inverter with insulated gate bipolar transistor (IGBT) power devices. Factors contributing to a motor overvoltage transient equal to a theoretical twice DC bus voltage are first described using existing transmission line analysis. A critical cable distance I_c is defined where this 2-pu overvoltage occurs. However, literature is lacking on flow motor voltage transients >2-pu bus voltage and up to 3-4 pu are generated. This phenomenon is observed on all PWM inverters with output cable lengths greater than l_c distance. Contributing factors to the >2-pu overvoltage phenomenon are investigated by exploring the complex interaction between drive modulation techniques, carrier frequency selected, cable natural frequency of oscillation, cable high-frequency damping losses, and, to a lesser extent, inverter output rise time. Theoretical calculations of cable frequency and damping are correlated with simulation and experimental results. Novel modifications to the PWM modulator, as well as external hardware apparatus, are proposed solutions to the >2-pu overvoltage problem; both are simulated and experimentally confirmed     

A new single ended fault location algorithm for combined transmission line considering fault clearing transients without using line parameters

In this paper a new single ended fault location method is proposed for underground cable combined with overhead lines. In this algorithm fault clearing high frequency transients are used instead of fault-generated transients and the line parameters are not needed. In the proposed algorithm, samples just from voltage transients generated by fault clearing action of circuit breaker are taken from the sending end of the cable line. Applying wavelet transform, the first three inceptions of traveling waves to the fault locator are detected. Using these, the proposed algorithm at first identifies fault section, overhead or cable, and then wave speed is calculated and at last location of fault is determined accurately. Because of using only voltage samples taken from one terminal, it is simple and economic and does not need to GPS and data communication and synchronization. Extensive simulations carried out using SimPowerSystem toolbox of MATLAB, confirm the capabilities and high accuracy of the proposed method under different system and fault conditions.     

Development of a positive creeping discharge along an aerial insulated wire

In high‐voltage aerial distribution systems, the insulated cables are supported by the binding wire with the post insulator at the utility pole. When a lightning strike occurs in the neighborhood of the insulated cable in an aerial power distribution system, inductive lightning surges invade the central line of the cable. Then, creeping discharges develop along the cable surface from the binding wire tip at the same time as flashover of the post insulator at a supporting point of the cable. If the cable insulator has weak points such as pinholes, a malfunction near the cable supporting point may occur, with melting of the wire due to punch‐through breakdown. To prevent such accidents, it is important to clarify the mechanism of the creeping discharge along the insulated cable caused by the lightning strike. The polarity of creeping discharges depends on the polarity of the inductive lightning surges, and the extension length and aspect of the discharge differ greatly depending on the discharge polarity. The development of these creeping discharges is attributed to complicated behavior of the positive and negative electric charges. In the present study, we examined in detail the development of a positive creeping discharge along a wire surface by using a high‐speed image converter camera. This paper describes the mechanism of development of a positive creeping discharge based on the experimental results. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 20–29, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20997     

电力电缆接头温度监控系统研究

现有的电力电缆接头温度在线监测报警系统存在测量数据传输距离受限制、检测装置供电困难、需进行大量现场施工建设成本过高等问题。文章结合城市地下电缆沟内电力电缆实际运行情况,经过分析论证,首次提出了以低功耗单片机为采集终端,以电力电缆为感应导体,用感应通信传输前端测量结果,再用GPRS通信模块将测量数据远距离传输到控制中心的新方案。该方案特别适用于地下电力电缆分布范围广、供电距离长的大中城市。     

XLPE电缆绕组的电路模型及其外半导电层暂态电压分布特性研究

以XLPE电缆为绕组的新型电力设备可能承受很高的暂态电压,而所用的XLPE电缆外部没有金属回流层,只有一层半导电层,因此深入了解其外半导电层的暂态特性很有必要.本文给出电缆绕组高频暂态下的电路模型,并将实际绕组的实测数据与仿真结果进行比较,两者吻合很好.这表明该电路模型可表达这类绕组外半导电层暂态时的表现,同时得出在冲击电压作用下,绕组前部的外半导电层是最薄弱部位及芯线与外半导电层间为电容耦合的结论.     

Parameter measurements to study surge propagation in induction machines

Winding failures in induction machines have been a major concern in the past several years, and more so recently with the addition of variable-speed drives (VSDs). Both the introduction of the vacuum breaker, and the use of pulsewidth-modulation (PWM) drives, utilizing fast switching insulated gate bipolar transistors, have resulted in an increase in winding failures in induction machines. Two mechanisms that cause winding failures are steep-fronted surges, like those caused during the opening and closing of vacuum breakers, and transient overvoltages caused by impedance mismatch between the cable and load during VSD operation. There has been a fair amount of work done to date on the propagation of vacuum-breaker-induced steep-fronted surges in the windings of the induction machine. More recently, work has been progressing on overvoltages at the machine terminals as a result of VSDs operating with long cables connecting the drive and machine. However, the propagation of these surges down the coils and the interference of these PWM surges with each other in the coils as well as the coupling between turns and coils have not been thoroughly investigated. Such an investigation would allow more benign PWM strategies to be developed, which do not build up in the machine to unacceptably high levels. The relevant parameters to be used are unknown and difficult to calculate and measure. To this end, this paper presents a measurement technique to determine the machine parameters for surge studies in machines. Detailed parameter measurements are made of each turn section (slot versus overhang), which are then used to determine the surge impedance of each section. Also included are the mutual capacitive and inductive couplings. Reflection and refraction coefficients are calculated which may then be used for further analysis of surges in machines.     

基于EMTP仿真平台的超高压电缆操作过电压特性及其影响研究

随着330 kV超高压电缆在西北电网的应用,暴露出电缆过电压特性方面仍存在诸多亟待解决的问题。首先在电磁暂态仿真（EMTP）平台建立典型的超高压电缆过电压仿真模型,对架空线和电缆线路中过电压的幅值变化研究对比,结果表明电缆线路的过电压幅值整体低于架空线路。然后应用模域回路理论对过电压的传播特性与主导频率特性进行分析,结果表明相同条件下,电缆线路操作过电压主导频率相对较低,传播模电压衰减严重,从而影响了过电压的最大值。仿真结果证明超高压电缆在形成操作过电压的同时,会导致下一级出线电缆送电端电压的稳定性受到影响。     

Capacitive voltage sensor for measuring very fast transient overvoltages in GIS

A reliable technique is needed for accurate measurement of very fast transient overvoltages such as disconnector-induced surges occurring in GIS which have very steep front and high-frequency oscillation. Recently, capacitive voltage sensors with very short response times have been proposed for this purpose. However, few studies have been made on the dielectric properties of materials used for a low-voltage-side capacitor, as well as the frequency bandwidth of the measuring system. In this paper a thin mica plate is proposed for a low-voltage-side capacitor which has a surface coated with silver on both sides. This material has been shown to have stable and high static capacitance up to a high-frequency range. A quantitative estimate also is given for the frequency bandwidth of the measuring system. Furthermore, a practical-scale sensor of this type has been developed which can successfully measure simulated disconnector-induced surges of several hundred kilovolts under similar conditions in GIS.     

Effect of surge voltage risetime on the insulation of low-voltagemachines fed by PWM converters

This paper investigates the repetitive surge-voltage withstand of low-voltage mush-wound machines operated on adjustable-speed drives (ASDs) using insulated gate bipolar transistor (IGBT) semiconductor technology. Historical work on surge testing of motor insulation has focused on one or more of the following aspects: (1) large horsepower motors; (2) medium-voltage form-wound motors; (3) single-shot impulse-type transients; or (4) low-voltage machines with surge risetimes >200 ns. IGBT drives can have risetimes of 50-200 ns. Thus, a new study on electrical stress of insulation systems due to the nonlinear voltage distribution of mush-wound motors when subjected to repetitive steep dV/dt square-pulse waveforms (rather than impulse wave testing) is presented. Magnitude and risetime of the repetitive ASD surge-voltage transient induced on the machine terminals is reviewed first. Next, surge propagation into the winding was investigated to identify maximum voltage stress points on the conductor insulation. Potential failure mechanisms observed at these points are then discussed. The significance of decreasing surge risetime and increasing cable lengths on internal nonlinear voltage distribution is studied with experimental results from a 7.5-hp motor with a tapped stator winding     

地铁直流电缆放电在线检测中干扰信号的研究

为解决地铁直流电缆电气接线的特殊性而导致其放电检测中存在的大量干扰信号,实验研究了整流装置产生的整流脉冲、机车启动制动产生的电流脉冲、随机性脉冲信号及其它电子设备产生的窄带信号等干扰信号的特征。研究表明,并联的被测电缆上均存在很好的整流脉冲干扰周期性和规律性;窄带干扰和机车反馈电流脉冲干扰幅值大但其频谱较低(<2MHz);随机脉冲干扰信号虽具有不确定性,但其重复率与电缆放电的重复率存在数量级差别。根据干扰信号特征提出了可行的抗干扰措施,为检测地铁直流电缆放电奠定了基础。     

气体绝缘变电站内电压互感器高频传输函数模型的建立

为了计算气体绝缘变电站 (GIS)内由开关操作等对二次设备产生的传导干扰 ,必须建立电压互感器、电流互感器的高频模型 (f≥ 10MHz) ,提出了通过拟和TV/TA传输函数的幅度平方函数得到该传输函数的新方法 ,并建立了某GIS电站内 170kV感应式TV从 1MHz到 6 0MHz高频传输函数模型。拟和方法采用了运算速度快、拟和结果准确、稳定的矢量匹配法     

Evaluation and testing of turn insulation of large AC motors

This paper reviews the results of tests performed on the stator windings of a 13.8 kV, 15000 HP variable speed slipring induction motor in order to assess its insulation condition and quantify the impulse strength of the motor winding. A surge voltage distribution test showed severe nonlinearity of turn voltage where up to 120% of the applied voltage was achieved across the first coil with 0.1-μs risetime. The effect of a surge capacitor was also demonstrated when a substantial reduction of the first coil voltage could be obtained at low risetime of 0.1 μs. Measurements of breakdown voltage (BDV) of coils at different locations gave indirect evidence that turn insulation degradation was most likely surge related. Finally, the paper contains a proposal of an alternative testing criteria to quantify impulse strength of turn insulation of large AC machines     

三相同壳结构GIS快速暂态过程模型构建和参数计算

数值计算模型和参数的确定,是三相同壳结构GIS快速暂态过程行波分析的基础.该文给出了三相同壳结构GIS快速暂态过程数值计算模型的构建方法.由于三相同壳结构GIS的最大特点是A、B、C三相之间存在电磁场耦合,模型的核心是电感矩阵和电容矩阵.分析表明,电感矩阵和电容矩阵中的所有元素,取决于GIS内导体半径和三相导体的偏心距离与GIS外壳内半径的相对比例.对于一般的三相同壳结构GIS,电感矩阵和电容矩阵的非对角线元素与对角线元素之比通常小于20%,对角线元素对快速暂态过程起主导作用;当忽略非对角线元素的作用时,可得到三相同壳结构GIS快速暂态过程的单相导体简化模型,以便对快速暂态过程进行定性的分析.但要对三相同壳结构GIS中VFT过电压进行定量分析,还应采用三相模型.     

雷电波侵入低压电源线引起冲击电压的仿真研究

针对雷电波侵入电力调度通信大楼电源线引起的冲击电压进行仿真研究,分别考虑不同的电缆接线方式、是否接压敏电阻以及压敏电阻的组数对冲击电压的影响。计算结果表明：未加装压敏电阻时,各结点电压随电缆长度的增加而升高;加装压敏电阻后,电缆沿线各结点冲击电压得到有效抑制;线路带负载后冲击电压进一步降低。在总配电柜及微电子设备的供电处各安装一组过电压保护器,可以有效降低冲击电压对大楼内微电子设备造成的危害。     

Varistor versus Environment: Winning the Rematch

An unusual case of difficult application of surge protective devices was solved by field measurements with retrofit of protective devices suitable for the particular environment. Onsite measurements indicated that capacitor switching transients were causing excessive current surges in the varistors and fuses protecting the input to a thyristor motor drive. Knowledge of the environment gained by the measurements allowed understanding of the problem and specification of matching surge protective devices.     

基于绝缘薄膜开关的快前沿高压方波发生器

本文对基于绝缘薄膜开关的方波脉冲发生器的设计及整体结构作了较详细的介绍,并分析了方波发生器放电回路杂散数对方波前沿的影响。整机可产生幅值1．5－8kV、前沿小于1．5ns、脉宽40ns的方波脉冲。     

On-site partial discharge measurements on premoulded cross-bondingjoints of 170 kV XLPE and EPR cables

A total number of 15 premoulded joints of three 170 kV cable circuits (XLPE and EPR) were equipped with partial discharge (PD) sensors. The developed sensors are based on inductive high frequency coupling of partial discharge pulses occurring in the joints. The PD activity of each joint was monitored during an after laying AC acceptance test. The test voltage of 190 kV was generated by means of a frequency-tuned series-resonance test set. The signals of the PD sensors were assessed with a spectrum analyser in a frequency range from 15 to 50 MHz, allowing a good separation of noise from PD signals under high interference levels. The investigation demonstrated the feasibility of on-site PD measurements on joints during after laying tests     

线缆负载连续波辐照效应仿真研究

基于电磁仿真软件CST,研究了电缆电长度、终端负载阻值、电场极化方向对终端响应电压的影响规律.结果表明,在某一频率条件下,在线缆单个电长度内,变化趋势基本相同,线缆负载响应电压幅值先是随着电缆长度的增加而变大,达到最大值后,响应幅值减小;随着频率的增大,响应幅值先增大后减小,谐振频率时响应值最大;随着终端电阻的增大,响...     

高效可逆变流器的自动定时控制算法

电流滞环控制系统中,开关高频化带来严重的开关损耗、电磁干扰和谐波污染。文章提出了自动定时控制的优化算法,将开关频率限定在一定范围内,以达到高效节能的目的;综合考虑交流侧感抗、开关频率、谐波畸变率和开关损耗等指标,提出了主电路电感参数和开关频率的选择公式,并采用TMS320F2812数字信号处理器构造了试验样机,进行仿真和试验研究,其结果证明了该方法的有效性和实用性。